#!./perl
# From Tom Phoenix 22 Feb 1997
# Based upon a test script by kgb@ast.cam.ac.uk (Karl Glazebrook)
# Looking for the hints? You're in the right place.
# The hints are near each test, so search for "TEST #", where
# the pound sign is replaced by the number of the test.
# I'd like to include some more robust tests, but anything
# too subtle to be detected here would require a time-consuming
# test. Also, of course, we're here to detect only flaws in Perl;
# if there are flaws in the underlying system rand, that's not
# our responsibility. But if you want better tests, see
# The Art of Computer Programming, Donald E. Knuth, volume 2,
# chapter 3. ISBN 0-201-03822-6 (v. 2)
BEGIN {
chdir "t" if -d "t";
@INC = qw(. ../lib);
}
use strict;
use Config;
require "test.pl";
plan(tests => 8);
my $reps = 10000; # How many times to try rand each time.
# May be changed, but should be over 500.
# The more the better! (But slower.)
sub bits ($) {
# Takes a small integer and returns the number of one-bits in it.
my $total;
my $bits = sprintf "%o", $_[0];
while (length $bits) {
$total += (0,1,1,2,1,2,2,3)[chop $bits]; # Oct to bits
}
$total;
}
# First, let's see whether randbits is set right
{
my($max, $min, $sum); # Characteristics of rand
my($off, $shouldbe); # Problems with randbits
my($dev, $bits); # Number of one bits
my $randbits = $Config{randbits};
$max = $min = rand(1);
for (1..$reps) {
my $n = rand(1);
if ($n < 0.0 or $n >= 1.0) {
print <= 1.0.
# Make sure \$Config{drand01} is a valid expression in the
# C-language, and produces values in the range [0.0,1.0).
#
# I give up.
EOM
exit;
}
$sum += $n;
$bits += bits($n * 256); # Don't be greedy; 8 is enough
# It's too many if randbits is less than 8!
# But that should never be the case... I hope.
# Note: If you change this, you must adapt the
# formula for absolute standard deviation, below.
$max = $n if $n > $max;
$min = $n if $n < $min;
}
# This test checks for one of Perl's most frequent
# mis-configurations. Your system's documentation
# for rand(2) should tell you what value you need
# for randbits. Usually the diagnostic message
# has the right value as well. Just fix it and
# recompile, and you'll usually be fine. (The main
# reason that the diagnostic message might get the
# wrong value is that Config.pm is incorrect.)
#
unless (ok( !$max <= 0 or $max >= (2 ** $randbits))) {# Just in case...
print < 0); # Next more positive int
unless (is( $off, 0 )) {
$shouldbe = $Config{randbits} + $off;
print "# max=[$max] min=[$min]\n";
print "# This perl was compiled with randbits=$randbits on $^O.\n";
print "# Consider using randbits=$shouldbe instead.\n";
# And skip the remaining tests; they would be pointless now.
print "# Skipping remaining tests until randbits is fixed.\n";
exit;
}
# This should always be true: 0 <= rand(1) < 1
# If this test is failing, something is seriously wrong,
# either in perl or your system's rand function.
#
unless (ok( !($min < 0 or $max >= 1) )) { # Slightly redundant...
print "# min too low\n" if $min < 0;
print "# max too high\n" if $max >= 1;
}
# This is just a crude test. The average number produced
# by rand should be about one-half. But once in a while
# it will be relatively far away. Note: This test will
# occasionally fail on a perfectly good system!
# See the hints for test 4 to see why.
#
$sum /= $reps;
unless (ok( !($sum < 0.4 or $sum > 0.6) )) {
print "# Average random number is far from 0.5\n";
}
# NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
# This test will fail .1% of the time on a normal system.
# also
# This test asks you to see these hints 100% of the time!
# NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
#
# There is probably no reason to be alarmed that
# something is wrong with your rand function. But,
# if you're curious or if you can't help being
# alarmed, keep reading.
#
# This is a less-crude test than test 3. But it has
# the same basic flaw: Unusually distributed random
# values should occasionally appear in every good
# random number sequence. (If you flip a fair coin
# twenty times every day, you'll see it land all
# heads about one time in a million days, on the
# average. That might alarm you if you saw it happen
# on the first day!)
#
# So, if this test failed on you once, run it a dozen
# times. If it keeps failing, it's likely that your
# rand is bogus. If it keeps passing, it's likely
# that the one failure was bogus. If it's a mix,
# read on to see about how to interpret the tests.
#
# The number printed in square brackets is the
# standard deviation, a statistical measure
# of how unusual rand's behavior seemed. It should
# fall in these ranges with these *approximate*
# probabilities:
#
# under 1 68.26% of the time
# 1-2 27.18% of the time
# 2-3 4.30% of the time
# over 3 0.26% of the time
#
# If the numbers you see are not scattered approximately
# (not exactly!) like that table, check with your vendor
# to find out what's wrong with your rand. Or with this
# algorithm. :-)
#
# Calculating absoulute standard deviation for number of bits set
# (eight bits per rep)
$dev = abs ($bits - $reps * 4) / sqrt($reps * 2);
ok( $dev < 3.3 );
if ($dev < 1.96) {
print "# Your rand seems fine. If this test failed\n";
print "# previously, you may want to run it again.\n";
} elsif ($dev < 2.575) {
print "# This is ok, but suspicious. But it will happen\n";
print "# one time out of 25, more or less.\n";
print "# You should run this test again to be sure.\n";
} elsif ($dev < 3.3) {
print "# This is very suspicious. It will happen only\n";
print "# about one time out of 100, more or less.\n";
print "# You should run this test again to be sure.\n";
} elsif ($dev < 3.9) {
print "# This is VERY suspicious. It will happen only\n";
print "# about one time out of 1000, more or less.\n";
print "# You should run this test again to be sure.\n";
} else {
print "# This is VERY VERY suspicious.\n";
print "# Your rand seems to be bogus.\n";
}
print "#\n# If you are having random number troubles,\n";
print "# see the hints within the test script for more\n";
printf "# information on why this might fail. [ %.3f ]\n", $dev;
}
# Now, let's see whether rand accepts its argument
{
my($max, $min);
$max = $min = rand(100);
for (1..$reps) {
my $n = rand(100);
$max = $n if $n > $max;
$min = $n if $n < $min;
}
# This test checks to see that rand(100) really falls
# within the range 0 - 100, and that the numbers produced
# have a reasonably-large range among them.
#
unless ( ok( !($min < 0 or $max >= 100 or ($max - $min) < 65) ) ) {
print "# min too low\n" if $min < 0;
print "# max too high\n" if $max >= 100;
print "# range too narrow\n" if ($max - $min) < 65;
}
# This test checks that rand without an argument
# is equivalent to rand(1).
#
$_ = 12345; # Just for fun.
srand 12345;
my $r = rand;
srand 12345;
is(rand(1), $r, 'rand() without args is rand(1)');
# This checks that rand without an argument is not
# rand($_). (In case somebody got overzealous.)
#
ok($r < 1, 'rand() without args is under 1');
}